Arrhyton albicollum DÍAZ, FONG, SALAS & HEDGES, 2021
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|Higher Taxa||Colubridae (Dipsadinae), Alsophiini, Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes)|
|Common Names||E: Gibara White-collared Racerlet|
|Synonym||Arrhyton albicollum DÍAZ, FONG, SALAS & HEDGES 2021|
Type locality: Entrance of Cueva de los Panaderos (21.105861, -76.138222, WGS84), Gibara, Holguín.
|Types||Holotype. MHNHCu 6000. Juvenile male. Collected by Alexis Silva García and José Raúl Suárez Bauzá on the 7th of January 2010.|
|Diagnosis||Diagnosis. A species of the genus Arrhyton, related to A. redimitum, as shown in the molecular phylogeny of Fig. 3. It can be distinguished from other species of the genus by the combination of (1) a wide immaculate white neck band or collar; (2) faint body stripes on a gray to grayish-tan background; (3) a solidly black and sharply defined cephalic pattern (“cap”, sensu Schwartz 1965), surrounded by whitish gray; (4) a short and solidly pigmented dark stripe crossing the eye, interrupted posteriorly by the white neck band, (5) a mucronate rostral scale (see Discussion), (6) high number of ventral scales (145), and high number of subcaudal scales (132).|
Most Arrhyton species have basically three well-defined body stripes on a tan or brown background, but there is variation in this character and two additional paravertebral stripes may be present depending on the species, giving some taxa a quinquelineate pattern (Fig. 1B–H). Arrhyton albicollum sp. nov. is closely related to A. redimitum. Juveniles of A. redimitum may have a pair of small occipital spots interrupted by the middorsal stripe or show narrow post-occipital indentations of the paler colored areas on either side of the middorsal stripe that abruptly disconnect the paravertebral stripes from the cephalic pattern (Figs. 1B and 2B–D). The cephalic “cap” is dark brown, generally paler in the middle and outlined dark in adults. The dark stripe across the eye from the sides of snout is continuous with the lateral stripe on each side, running along the body to the tail. None of the available specimens of A. redimitum has a conical, abrupt, dark projection on the rostral scale. Like most A. redimitum, A. albicollum sp. nov. has a dark spot on each of the internasal scales and stippled first labials. The ventral scale count of A. albicollum sp. nov. (145) is within the range of A. redimitum. However, only the holotype (MCZ 42505) of A. landoi (= A. redimitum) has 150 ventrals, the remaining sampled individuals of this species have 110–144 (mean 128, n = 54) ventrals. The number of subcaudal scales of A. albicollum sp. nov. is higher than that of A. redimitum (63–125, mean 89, n = 44; specimens with missing tail tips were not included).
Arrhyton dolichura (Figs. 1C and 2F), A. procerum (Figs. 1D and 2G), and A. tanyplectum (Figs. 1F and 2J, K), have long tails which are 40–46% of the TL versus 25–40% of the TL of other species (39% in A. albicollum sp. nov.). These snakes have well defined stripes, and usually a vivid yellow or cream coloration on the lower flanks and the belly. In none of them is the cephalic dorsal pattern or “cap” solid black (as in A. albicollum sp. nov.) and the number of subcaudal scales of A. albicollum sp. nov. is in the range of A. tanyplectum (Table 1). Arrhyton ainictum has a well-defined quinquelineate pattern, 137 ventrals (vs. 145 in A. albicollum sp. nov.), 108 subcaudals (versus 132), and shorter tail which is 33% of TL (vs. 39%).
Arrhyton vittatum (Figs. 1G and 2L) is easily distinguished from A. albicollum sp. nov. and the other species of Arrhyton in that it has a reddish brown coloration. The middorsal stripe may be absent, paler, or wider than those stripes on the flanks. Intercalated paravertebral stripes are sometimes slightly evident or generally absent in this species. The ventral coloration is pearl-white to iridescent grayish-pink. Juveniles may have some evidence of small occipital pale spots; the dark cephalic dorsal pattern is diffuse in adults (“soot-like”), not conspicuously surrounded by a distinctive pale coloration, and the snout is mostly pale brown. The number of ventral (107–123) and subcaudal (52–81) scales is notably lower than A. albicollum sp. nov. (Table 1) and the tail is shorter, 29–33% TL (vs. 39%).
Arrhyton supernum (Figs. 1E and 2H) has two occipital pale spots, instead of a broad white band, interrupted by the middorsal stripe; the overall coloration is dark brown, compared with the grayish color of A. albicollum sp. nov., the number of ventral (124–128) and subcaudal (107–108) scales is much lower (Table 1), and the tail is 26% TL (vs. 39%).
Arrhyton taeniatum (Figs. 1H and 2I) is the largest species (up to 457 mm SVL, MNHNCu 4622) and it occurs syntopically with A. albicollum sp. nov. It is the only species which always lacks a loreal scale. It has wide body stripes that in some individuals are indistinct from the brown background, vivid yellow flanks and belly, the highest number of ventral scales (168–189, vs. 145 in A. albicollum sp. nov.), a projected and upturned rostral scale, a laterally expanded head and smaller eyes which are far from the head outline when seen dorsally vs. larger and slightly protruded eyes from the head outline in A. albicollum sp. nov. (Diaz et al. 2021).
Color in life: Dorsum gray to grayish-tan, with faint stripes. Each scale with somewhat darker pigmentation on the edge giving the overall dorsal region a net-like appearance. The neck band is immaculate white, and behind it there is a slightly darker, smoky-gray pigmentation that transitions to the dorsal color. Internasal scales with a dark spot on each. Another dark spot is present on each prenasal scale. First three supralabials and four infralabials stippled with dark brown. Rostral conical projection dark. Eye bicolored: upper half grayish-white; inferior half very dark brown, almost black. Venter paler than dorsum. A faint lateral stripe on scale row four, just defined by slightly darker pigmentation of scale borders, giving a serrated outline and bordered at the top by a narrow zone paler than the rest of the dorsum.
Color in alcohol (ten years after collection): similar to coloration in life, except that yellowish pigments completely disappeared. The faint stripes are even less obvious (Diaz et al. 2021).
|Comment||Distribution: see map in Díaz et al. 2021: Fig. 5.|
|Etymology||The specific epithet is derived from the Latin words albus (white) and collum (neck), in reference to the conspicuous white neck band|
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